Known tandem drive vehicles, for example, may use suspensions incorporating equalising beams and leaf springs to cushion road shocks and to distribute weight equally between the tandem drive axles and transport wheels mounted thereon thereby improving traction. The springs are generally mounted on saddle assemblies above the equalising beams and connected at the front ends to front spring hangers with spring eye pins or spindles (hereinafter called "spring pins") through the spring eyes. The rear ends of the springs have no rigid attachment to the rear spring hangers and they are usually free to move forward and backward to accommodate spring deflection. The rear hangers may be provided with cam surfaces which allow for this movement of the spring. Spring hangers may be affixed to the frame or chassis of the vehicle by conventional fixing means such as bolts, washers and nuts.
It is generally seen to be of great advantage that the tandem drive axles be parallel to each other and properly aligned with respect to the longitudinal axis of the truck frame or chassis. Prior suspension systems have been found wanting in satisfactory means for adjustment of the alignment of the axle with respect to the vehicle frame or chassis. The Zneed for such adjustment has arisen in the last 2-3 years as a result of improvements in alignment measurement techniques, especially as a result of using laser-based equipment. If the axles and the wheels are properly aligned with the longitudinal axis of the vehicle frame, tire wear may be minimised and significant savings in fuel consumption may also be achieved.
Two methods have been developed in an effort to provide some form of alignment adjustment. Those methods have involved on the one hand to altering the position of the saddle assembly with respect to the leaf spring assembly and on the other hand, the fitting of an eccentric adaptor at the ends of the equalising beams where they are attached to the vehicle axles. The former method is time consuming and arduous as it usually involves disassembling the saddle assembly and the leaf spring assembly.